Various attempts are made in regard to realization of high picture quality of television. For example, a conversion to a progressive scanning system, etc. shown in "High Quality Digital Television" (Toshiba Review, Vol. 42, No. 12, 1987) is a representative system. In accordance with this system, in converting an interlaced scanning television signal to progressive or sequential scanning (i.e., non-interlaced scanning) television signal, when there is a motion in a pictorial image, an interpolation signal is generated on the basis of signals within each field, and while when there is no movement in a pictorial image, an interpolation signal is generated on the basis of signals over a plurality of fields. This system is called a motion adaptive scanning line interpolation. Since implementation of such a conversion can result in improved vertical resolution and reduced flicker, the picture quality of the television can be improved to much extent.
FIG. 3 is a block diagram of an image signal processing device as the background art for realizing such a scanning line interpolation. Especially, there is shown an arrangement to respectively interpolate a luminance signal and a color signal in accordance with different systems, thus converting an interlaced scanning television signal to a progressive scanning television signal.
As shown in FIG. 3, a television signal is inputted as separate signal inputs of a luminance signal input Y.sub.IN and a color signal input C.sub.N. The luminance signal input Y.sub.IN thus inputted is delayed by one horizontal scanning period through an 1H delay line 2. Further, this luminance signal input Y.sub.IN is delayed by a time period corresponding to one field through a field memory 4. Namely, the signal obtained from the field memory 4 is a signal obtained by delaying the luminance signal input Y.sub.IN by a time period corresponding to one field. On the other hand, the luminance signal input Y.sub.IN is added to an output from the 1H delay line 2, i.e., a luminance signal input Y.sub.IN preceding 1H before at an adder circuit 6, and is then halved at a 1/2 circuit 8. Namely, an output from the 1/2 circuit 8 is an average value of the luminance signal input Y.sub.IN and the luminance signal input Y.sub.IN preceding 1H before. A selection circuit 10 selects either an output from the field memory 4 or an output from the 1/2 circuit 8 by a motion control signal M outputted from means (not shown) in correspondence with motions of a pictorial image of the television signal. Namely, when there is a motion in a television image, the selection circuit 10 selects an output from the 1/2 circuit 8, while when there is no motion in that image, it selects an output from the field memory 4, i.e., a signal preceding one field before. The luminance signal input Y.sub.IN and an output from the selection circuit 10 are inputted to first in first out (FIFO) circuits 12Y and 14Y, respectively. These circuits alternately output by a time period corresponding to 1H on the basis of a scan rate of the progressive scanning. Namely, by switching a changeover switch 16Y to alternately take out the both outputs, a luminance signal output Y.sub.OUT for forming a non-interlaced frame can be provided.
On the other hand, the inputted color signal input C.sub.IN is inputted to an 1H delay line 18. The color signal input C.sub.IN is added to a color signal input C.sub.IN delayed by 1H which is an output from the 1H delay line 18 at an adder circuit 20. An output from the adder circuit 20 is inputted to a 1/2 circuit 22. Thus, an average value of the original color signal input C.sub.IN and the color signal input C.sub.IN delayed by 1H is provided from the 1/2 circuit 22. Furthermore, an output from the 1H delay line 18 and an output from the 1/2 circuit are inputted to FIFOs 12c and 14c, respectively. Thus, a color signal output C.sub.OUT is provided through a switch 16c in a manner similar to the above. Namely, by switching of the switch 16c, outputs from the FIFOs 12c and 14c are alternately outputted. That is, an output from the FIFO 12c is outputted as a color signal of the line signal, and an output from the FIFO 14c is outputted as a color signal of the interpolation line.
The operation and the effect of the device thus constructed will be described in more detail with reference to FIGS. 4A to 4C. FIG. 4A is an explanatory view of a television frame. In this figure, there is shown the manner in which a plurality of horizontal scanning lines n, n+1, n+2, n+3, n+4, . . . are arranged in a vertical direction V to form one frame. In the case of a typical interlaced scanning, the horizontal scanning lines n, n+2, n+4, . . . and the horizontal scanning lines n+1, n+3, . . . belong to different fields, respectively, and are displayed on the screen at one field time interval of the television signal. On the contrary, in the progressive scanning system, the horizontal scanning lines n, n+1, n+2, n+3, n+4, . . . are all displayed as one frame. For this reason, it is required to generate signals of interpolation horizontal scanning lines for filling the interlaced scanning portions by interpolation, etc. FIGS. 4B and 4C show the relationship of the amplitudes of respective horizontal scanning lines n, n+1, n+2, n+3, n+4, . . . In these figures, there are shown the relationship between the amplitudes of actual scanning lines (solid lines) of a luminance signal and the amplitudes of interpolation scanning lines (broken lines) thereof and the relationship between the amplitudes ( ) of actual scanning lines of a color signal and the amplitudes (.largecircle.) of interpolation scanning lines thereof, respectively.
In the above-mentioned background art, motion-adaptive interpolation is applied to the luminance signal. A motion-adaptive interpolation signal is obtained from a motion detection circuit (not shown). Switching of the selection circuit 10 by this motion control signal M leads to switching of the motion-adaptive operation.
When there is no motion in a television image, the selection circuit 10 selects an output from the field memory 4 to synthesize two fields into one non-interlaced frame through FIFOs 12Y and 14Y to output the synthesized frame. Namely, since a pictorial image including no motion has an extremely high correlation between fields, interfield interpolation is carried out.
On the contrary, in the case where there is a motion in a television image, since pictorial images of respective fields are naturally different to one another, an intraframe interpolation is carried out. In the intrafield interpolation, two horizontal signals of interlaced scanning are added by the 1H delay line 2 and the adder circuit 6. An average value of the added signal is taken at the 1/2 circuit 8. Thus, an interpolation signal between lines is provided. This interpolation signal is selected by a motion control signal M at the selection circuit 10, and is then inputted to the FIFO circuit 14Y. As a luminance signal output Y.sub.OUT, a progressive scanning signal which has been subjected to intrafield interpolation is provided.
On the other hand, in the case of a color signal, only an intrafield interpolation is implemented thereto irrespective of whether or not there is a motion. Namely, two horizontal signals of interlaced scanning of the color signal input C.sub.IN are added by the 1H delay line 18 and the adder circuit 20. An average value of the added signal is taken at the 1/2 circuit 22. Thus, an interpolation signal between lines is provided. This interpolation signal is outputted as a progressive scanning color signal output C.sub.OUT through FIFOs 12c and 14c. Thus, a progressive scanning signal which has been subjected to intrafield interpolation is provided.
The image signal processing device of the background art has been constructed above. For this reason, where an intrafield interpolation is carried out, both the luminance signal and the color signal generate interpolation signals on the basis of the correlation with upper and lower lines of the horizontal scanning signal, resulting in no extreme separation between the luminance signal and the color signal. On the contrary, in the case where an interfield interpolation of the luminance signal is carried out on a frame in which there is less motion, there may be produced a difference resulting from a difference between interpolation schemes for the luminance signal and the color signal. Namely, when a television screen is viewed along the line A of FIG. 4A, there may occur instances where the luminance signal level varies rapidly in a vertical direction between an interpolated line and the upper or lower actual line as shown in FIGS. 4B and 4C. On the contrary, since only an intrafield interpolation is implemented to the color signal, only a level of an average value between actual lines occurs as a level of an interpolated line. This leads to the problem that color bleeding and color missing may occur in the cases of FIGS. 4B and 4C, respectively. Thus, spreading in upper and lower directions of color considerably lowers the quality of an image. On the other hand, while it is sufficient for the color signal to detect its motion to employ an interpolation method similar to that of the luminance signal, this results in the problem that the configuration becomes complicated, leading to an extremely high cost.